Method, system and apparatus for accessing a visited network

ABSTRACT

The embodiments of the present invention disclose a method for accessing a visited network. The method includes: a user selects a visited network and initiates an access request to a user information application apparatus; when the user information application apparatus detects that the visited network has changed, it obtains a list of authorized visited networks from a user information storage apparatus and checks whether the user is authorized to access the visited network; or the user information storage apparatus checks whether the user is authorized to access the visited network; if the user is authorized to access the visited network, the user information application apparatus returns an access accept response to the user, allowing the user to access the visited network. The embodiments of the present invention also disclose systems and apparatuses for accessing a visited network. The embodiments of the present invention make it possible to accurately check whether the user is authorized to access a visited network.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of PCT Application No.PCT/CN2006/001771, filed on Jul. 20, 2006, which claims a priority toChinese Patent Application No. 200510090294.2, filed on Aug. 12, 2005.All of these applications are incorporated herein by reference for allpurposes.

FIELD OF THE INVENTION

The present invention relates to wireless telecommunication networks,and more particularly, to a method, a system and an apparatus foraccessing a visited network.

BACKGROUND OF THE INVENTION

As users require higher and higher radio access rate, wireless localarea network (WLAN) emerges accordingly to meet the requirement. TheWLAN can provide high speed wireless data access in a smaller range. TheWLAN includes various access technologies. At present, IEEE 802.11b is awidely used technical standard. It transmits in the 2.4 GHz band, andthe maximum transmission rate may reach 11 Mbps. IEEE 802.11g andBluetooth technology also transmits in the 2.4 GHz band, of which themaximum data transmission rate of IEEE 802.11g may reach 54 Mbps. Othernew technologies such as IEEE 802.11a and ETSI BRAN Hiperlan2 use the 5GHz band, and the transmission rate may reach up to 54 Mbps.

In spite of various radio access technologies, most WLANs are used totransmit Internet protocol (IP) packets. In general, the WLAN accesstechnology used by a wireless IP network is transparent for theupper-layer IP. The basic principle is that an access point (AP) is usedto complete the access of user equipment (UE), network control equipmentand connection equipment are connected to form an IP transmissionnetwork.

With emergence and development of the WLAN technology, interworkingbetween WLAN and wireless mobile communication networks such as GSMsystem, CDMA system, WCDMA system, TD-SCDMA system and CDMA2000 systemis becoming a research focus currently. In the 3rd GenerationPartnership Project (3GPP), a UE may be connected to Internet orIntranet through a WLAN access network. It can also be connected to ahome network or a visited network of the 3GPP system via a WLAN accessnetwork. To be specific, when a UE accesses to a WLAN locally, it isconnected to the home network of 3GPP via the WLAN access network; whenthe UE is roaming, it is connected to the visited network of 3GPP viathe WLAN access network. Some entities in the visited network of 3GPPare connected with corresponding entities in the home network of 3GPP.For example, the authentication, authorization and accounting (AAA)proxy in the visited network of 3GPP is connected with the AAA serverwhich is located in the home network of 3GPP; the WLAN access gateway(WAG) which is located in the visited network of 3GPP is connected withthe packet data gateway (PDG) which is located in the home network of3GPP.

Due to mobility of a user in wireless networks, the user often needs toaccess services during roaming, which results in the following twosituations:

1. When a user is roaming, there may be multiple roaming (or visited)networks available. Due to the agreements between the home network ofthe user and the roaming networks, the user may not access all of theavailable networks. In this case, when the user selects a roamingnetwork to access, the home network would authenticate the roamingnetwork. Namely, the home network needs to check whether the user isauthorized to access the roaming network selected by the user. In thisprocedure, in the home network, it involves storage, transfer and use ofinformation of roaming networks which the user are authorized to access.

2. To reduce the possibilities of a user selecting a network which it isnot authorized to access, the information of the authorized visitednetwork may be stored in the UE. Due to technical and operationalreasons, the information stored in the UE may be nonsynchronous with thecurrent authorized visited networks. In this case, the information ofthe authorized visited networks stored in the UE need to be updated.

In the prior technology, the information of authorized visited networksfor the user to access is stored only in the home subscriber server(HSS). When a user selects a visited network during roaming andinitiates an access authentication and/or authorization request, the AAAserver initiates a request to the home HSS for obtaining authenticationand/or authorization information if it checks that the authenticationand/or authorization information for the user is not stored locally.

Based on the stored information of authorized visited networks for theuser to access, if the HSS finds that the user is authorized to accessthe visited network, the HSS delivers at least one group of securityparameters for authenticating and corresponding authorizationinformation to the AAA server.

The AAA server stores the security parameters and correspondingauthorization information locally.

When the user selects another visited network and initiates anauthorization and/or authentication request, the AAA server does notinitiate a request for obtaining authentication and authorizationinformation to the HSS after checking that the security parameters forauthenticating the validity of the user is stored locally. As the AAAserver does not store the information of the authorized visited networksfor the user to access, it cannot check whether the user can access thevisited network.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a method for accessing avisited network to solve the problem that when a user access a visitednetwork, network side cannot correctly check whether the user isauthorized to access the visited network in the prior technology.

According to the method provided in the embodiments of the presentinvention, the embodiments of the present invention provide a userinformation application apparatus and a user information storageapparatus and a system for accessing a visited network.

Embodiments of the present invention provide a method for accessing avisited network; the method may include the following steps:

A user initiates an access request to a user information applicationapparatus for selecting a visited network.

The user information application apparatus detects whether the visitednetwork selected by the user has changed, if the visited networkselected by the user has changed; the user information applicationapparatus performs the following steps:

The user information application apparatus obtains a list of authorizedvisited networks from a user information storage apparatus and checkswhether the user is authorized to access the visited network accordingto the information of the list of authorized visited networks; or theinformation application apparatus ask the user information storageapparatus to check whether the user is authorized to access the visitednetwork.

If the user is authorized to access the visited network, the userinformation application apparatus returns an access accept response tothe user, allowing the user to access the visited network.

For example, the access request is an authentication and/orauthorization request, and the access accept response is anauthentication and/or authorization accept response.

The step of the user information storage apparatus checking whether theuser is authorized to access the visited network may include thefollowing steps concretely:

The user information application apparatus sends an acknowledgmentrequest containing an identifier of the visited network selected by theuser to the user information storage apparatus.

If checking that the user is authorized to access the visited networkaccording to the list of authorized visited networks, the userinformation storage apparatus returns an access accept response to theuser information application apparatus.

The above method of the embodiment of the invention may further includethe following steps:

The user information application apparatus initiates a request forobtaining authentication and/or authorization information to the userinformation storage apparatus and for requesting whether the user isauthorized to access the visited network. The user information storageapparatus returns the authentication and/or authorization information ofthe user and an access accept or reject response to the user informationapplication apparatus in accordance with the request.

The above method of the embodiment of invention may further include thefollowing the steps:

The user information application apparatus checks whether theauthentication and/or authorization information of the user is storeduser in the information application apparatus. If the authenticationand/or authorization information of the user is stored in theinformation application apparatus, the user information applicationapparatus sends an acknowledgement request containing the identifier ofthe visited network to the user information storage apparatus. The userinformation storage apparatus returns an access accept or rejectresponse to the user information application apparatus in accordancewith the acknowledgement request.

If the authentication and/or authorization information of the user isnot stored in the information application apparatus, the userinformation application apparatus initiates a request to the userinformation storage apparatus, for obtaining the authentication and/orauthorization information and for asking the user information storageapparatus to check whether the user is authorized to access the visitednetwork. The user information storage apparatus returns theauthentication and/or authorization information of the user and anaccess accept or reject response to the user information applicationapparatus in accordance with the request.

According to the above method of the embodiment of the invention, theacknowledgement request sent by the user information applicationapparatus via a customized signaling message or idle or new parametersin an existing protocol signaling message to the user informationstorage apparatus.

The above method of the embodiment of invention further includes:

The user information application apparatus checks whether theauthentication and/or authorization information of the user is storedlocally. If the authentication and/or authorization information of theuser is stored locally, the user information application apparatusinitiates a request for obtaining the list of visited networksauthorized for the user. The user information storage apparatus sendsthe list of visited networks authorized for the user to the userinformation application apparatus.

If the authentication and/or authorization information of the user isnot stored locally, the user information application apparatus initiatesa request for obtaining the authentication and/or authorizationinformation to the user information storage apparatus and requests toobtain the list of visited networks authorized for the user. The userinformation storage apparatus returns the locally stored authenticationand/or authorization information of the user and the list of visitednetworks authorized for the user to the user information applicationapparatus.

The above method of the embodiment of the invention may further includethe following steps:

The user sends a request for updating the list of authorized visitednetworks to the user information application apparatus according to apreset period.

After checking that the user is valid, the user information applicationapparatus sends the locally stored list of visited networks authorizedfor the user or the list of visited networks authorized for the user toaccess obtained from the user information storage apparatus to the user.

The above method of the invention further includes:

The user information storage apparatus sends a notification for updatingthe list of visited networks authorized for the user to access to theuser information application apparatus.

If checking that the user is online, the user information applicationapparatus forwards the update notification to the user.

After receiving the update notification, the user sends a request forupdating the list of authorized visited networks to the user informationapplication apparatus.

The user information application apparatus obtains the list ofauthorized visited networks from the user information storage apparatusand sends the list to the user.

The above method of the embodiment of the invention may further includethe following steps:

The user information storage apparatus pushes the list of authorizedvisited networks to the user information application apparatus.

The user information application apparatus pushes the received list ofauthorized visited networks to the user.

The list of visited networks authorized for the user includes authorizedvisited access networks and/or authorized visited core networks.

According to the above method of the embodiment of the invention, whendetecting that the visited network selected by the user has not changed,the user information application apparatus performs the regularauthentication and/or authorization flow in the prior technology.

The embodiment of the invention provides a user information applicationapparatus, including an authentication and authorization module, adetecting module and a checking module.

The authentication and authorization module is adapted to receive anaccess authentication and/or authorization request initiated by a userwhen the user selects a visited network, check whether the user is validaccording to the authentication and/or authorization information of theuser, and return an authentication and/or authorization accept or rejectresponse to the user according to the result of checking whether theuser is authorized to access the visited network by the checking module.

The detecting module is adapted to detect whether the visited networkselected by the user has changed. When the visited network has changed,the checking module is triggered.

The checking module is adapted to obtain a list of authorized visitednetworks from a user information storage apparatus and check whether theuser is authorized to access the visited network according to theinformation of the list of the authorized visited networks; or thechecking module is adapted to request the user information storageapparatus to check whether the user is authorized to access the visitednetwork and send the checking result to the authentication andauthorization module.

According to the user information application apparatus provided by theinvention, the checking module includes:

An obtaining sub-module, which is adapted to obtain the list of visitednetworks authorized from the user information storage apparatus andstores it;

A checking sub-module, which is adapted to check whether the user isauthorized to access the visited network according to the obtained listof authorized visited networks;

A sending sub-module, which is adapted to send the checking result ofthe checking sub-module to the authentication and authorization module.

In another embodiment of the invention, the checking module may include:

A requesting sub-module, which is adapted to send an acknowledgmentrequest message containing the identifier of the visited network to theuser information storage apparatus, asking the user information storageapparatus to check whether the user is authorized to access the visitednetwork;

A receiving sub-module, which is adapted to receive the result ofchecking whether to allow the user to access the visited network by theuser information storage apparatus;

A sending sub-module, which is adapted to send the checking result ofthe user information storage apparatus to the authentication andauthorization module.

The user information application apparatus, for example, is anindependent network entity with external interfaces or a logical unit ofan existing network entity.

The existing network entity, for example, is a 3GPP AAA server.

The embodiment of the present invention provides a user informationstorage apparatus, including a storage module and an information sendingmodule.

The storage module stores a list of visited networks authorized andauthentication and/or authorization information of the user.

The information sending module is adapted to send the list of authorizedvisited networks and authentication and/or authorization information ofthe user to the user information application apparatus in accordancewith a request of the user information application apparatus.

The user information storage apparatus provided by the embodiment of theinvention may further include an acknowledging module.

The acknowledging module is adapted to receive an acknowledgment requestmessage containing the identifier of the visited network from the userinformation application apparatus, check whether the user is authorizedto access the visited network according to the list of authorizedvisited networks stored in the storage module, and send the checkingresult to the information sending module. The information sending modulethen sends the checking result to the user information applicationapparatus.

The user information storage apparatus for example, is an independentnetwork entity with external interfaces or a logical apparatus of anexisting network entity.

The existing network entity, for example, is a home location register(HLR) or an HSS.

The embodiment of the present invention provides a system for accessinga visited network, which includes a user information applicationapparatus and a user information storage apparatus.

The user information application apparatus includes an authenticationand authorization module, a detecting module and a checking module.

The authentication and authorization module is adapted to receive anaccess authentication and/or authorization request initiated by a userwhich selects a visited network, check whether the user is validaccording to the authentication and/or authorization information of theuser, and return an authentication and/or authorization accept or rejectresponse to the user according to the result of checking whether theuser is authorized to access the visited network by the checking module.

The detecting module is adapted to detect whether the visited networkhas changed. When the visited network has changed, the checking moduleis triggered.

The checking module is adapted to obtain a list of authorized visitednetworks from the user information storage apparatus and check whetherthe user is authorized to access the visited network according to theinformation of the list of authorized visited networks; or the checkingmodule is adapted to request the user information storage apparatus tocheck whether the user is authorized to access the visited network andsend the checking result to the authentication and authorization module.

The user information storage apparatus may include a storage module andan information sending module.

The storage module is adapted to store the list of authorized visitednetworks and the authentication and/or authorization information of theuser.

The information sending module is adapted to send the list of authorizedvisited networks and authentication and/or authorization information ofthe user to the user information application apparatus in accordancewith the request of the user information application apparatus.

According to the above system provided by the embodiment of the presentinvention, the user information storage apparatus may further include anacknowledging module.

The acknowledging module is adapted to receive an acknowledgment requestmessage containing the identifier of the visited network selected by theuser from the user information application apparatus, check whether theuser is authorized to access the visited network according to the listof authorized visited networks. The information sending module isadapted to send the checking result to the user information applicationapparatus. Many benefits may be achieved by way of the embodiments ofthe present invention, for example:

1. When a user selects a visited network and initiates an authenticationand authorization request, there is provided a complete authenticationand authorization signaling flow, which can effectively check whetherthe user is authorized to access the visited network.

2. The embodiments of the invention also provides multiple methods forupdating the list of visited networks stored in the UE so that the listcan be updated synchronously with the visited networks authorized by theoperator for the user to access.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with an embodiment of the presentinvention

FIG. 2 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with another embodiment of the presentinvention.

FIG. 3 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with a further embodiment of the presentinvention.

FIG. 4 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with a further embodiment of the presentinvention.

FIG. 5 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with a further embodiment of the presentinvention.

FIG. 6 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with a further embodiment of the presentinvention.

FIG. 7 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with a further embodiment of the presentinvention.

FIG. 8 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with a further embodiment of the presentinvention.

FIG. 9 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with a further embodiment of the presentinvention.

FIG. 10 shows a simplified flowchart illustrating a method for updatinga list of authorized visited networks for the user to access accordingto an embodiment of the present invention.

FIG. 11 shows a simplified flowchart illustrating a method for updatinga list of authorized visited networks for the user to access accordingto an embodiment of the present invention.

FIG. 12 shows a simplified flowchart illustrating a method for updatinga list of authorized visited networks for the user to access accordingto an embodiment of the present invention.

FIG. 13 shows a schematic diagram of a user information applicationapparatus according to an embodiment of the present invention.

FIG. 14 shows a schematic diagram of a user information storageapparatus according to an embodiment of the present invention.

FIG. 15 shows a schematic diagram of a system according to an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention provide a method for accessinga visited network. The method may include the following steps:

A user selects a visited network and initiates an access request to auser information application apparatus.

The user information application apparatus detects whether the visitednetwork selected by the user has changed. When the visited networkselected by the user has changed, the user information applicationapparatus obtains a list of authorized visited networks from a userinformation storage apparatus and checks whether the user is authorizedto access the visited network according to the information of the listof authorized visited networks; or the user information storageapparatus checks whether the user is authorized to access the visitednetwork.

If the user is authorized to access the visited network, the userinformation application apparatus returns an access accept response tothe user, allowing the user to access the visited network; otherwise,the user information application apparatus returns an access rejectresponse, not allowing the user to access the network.

In the embodiments of the present invention, a list of authorizedvisited networks for a user to access is stored in a user informationstorage apparatus at the network side. When a user initiates a requestfor authentication and/or authorization to a user informationapplication apparatus at the network side through a radio access network(RAN), the following two methods are available for achieving thisobjective:

Method 1: The user information application apparatus downloads the listof authorized visited networks for the user to access, and checkswhether the user is authorized to access the visited network. The stepsare as follows:

Step A: The user information application apparatus checks whether theuser is valid and obtains the list of authorized visited networks fromthe user information storage apparatus.

Step B: The user information application apparatus checks whether theuser is authorized to access the visited network according to the listof authorized visited networks. If the user is valid and authorized toaccess the visited network, the user information application apparatusreturns an authentication and/or authorization accept response;otherwise, it returns an authentication and/or authorization rejectresponse.

Method 2: Storing the list of authorized visited networks for the userto access in the user information storage apparatus and the userinformation storage apparatus checks whether the user is authorized toaccess the visited network. The steps are as follows:

Step a: The user information application apparatus detects whether thevisited network selected by the user has changed. If yes, the procedurecontinues with the following steps; otherwise, the procedure continuesaccording to the authentication and/or authorization flow in the priorart.

Step b: The user information application apparatus sends anacknowledgment request to the user information storage apparatus,requesting the user information storage apparatus to check whether theuser is authorized to access the visited network.

Step c: The user information storage apparatus checks whether the useris authorized to access the visited network according to the list ofauthorized visited networks stored in the user information storage; andreturns an access accept or a reject response to the user informationapplication apparatus.

Step d: If the user information application apparatus receives an accessaccept response returned by the user information storage apparatus, andchecks that the user is valid, it returns an authentication and/orauthorization access accept response to the user; otherwise, it returnsa reject response.

The above two methods are hereinafter described in detail with referenceto the following embodiments and accompanying drawings.

FIG. 1 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with an embodiment of the presentinvention. The method may include the following steps:

Step 1 a: A RAN and a user information application apparatus perform anaccess authentication and authorization procedure for a UE.

If an identifier of the visited network selected by the user (UE)exists, it is sent to the user information application apparatus ifnecessary. For example, the identifier of the WLAN selected by the userto access the network is a home WLAN identifier in the case ofnon-roaming or a roaming WLAN identifier in the case of roaming. In thecase of roaming, the authentication and/or authorization requestcontains the identifier of visited network selected by the user and theuser's permanent or temporary identity. In the step, the userinformation application apparatus is often an AAA server.

The visited network identifier may include the identifier of the visitedaccess network and/or the identifier of the visited core network

For example, in a 3GPP I-WLAN (Interworking-WLAN) system, the visitednetwork identifier may include an identifier of a 3GPP visited publicland mobile network (PLMN), or a identifier of a visited WLAN, or bothof them.

For example, in a WiMax system, the visited network identifier mayinclude a identifier of a visited connectivity service network (CSN), ora identifier of a visited access service network (ASN), or both of them.

The format of a visited network identifier includes but is not limitedto the following formats:

-   -   Mobile country code (MCN)+Mobile network code (MNC);    -   RADIUS Operator-Name attribute; format specified in GSMA PRD        IR.61;    -   Network identifier defined by operators.    -   A user's identity includes but is not limited to the following:    -   International mobile subscriber identity (IMSI)        Mobile station international ISDN number (MSISDN)    -   Network access identifier (NAI)    -   Temporary mobile subscriber identity (TMSI) or packet TMSI        (P-TMSI)    -   SIP URI;    -   Tel URI

User's Identity Defined by Operators

Step 1 b: The user information application apparatus obtains userinformation from the user information storage apparatus forauthentication and/or authorization. The user information includes thelist of authorized visited networks for the user to access.

The list of authorized visited networks may include authorized visitedaccess network identifiers and/or authorized visited core networkidentifiers.

For example, the list of authorized visited networks for the user toaccess may include authorized 3GPP visited PLMN identifiers, orauthorized visited WLAN identifiers, or both of them. Optionally, it mayinclude the mapping between the authorized 3GPP visited PLMN identifiersand the authorized visited WLAN identifiers.

For example, the list of visited authorized networks may includeauthorized visited CSN identifiers, or authorized visited ASNidentifiers, or both of them. Optionally, it may include the mappingbetween the authorized visited CSN identifiers and the authorizedvisited ASN identifiers.

In the step 1 b, for example, the user information storage apparatus inthe 3GPP system is often an HLR or an HSS.

In this embodiment, for example, the user information storage apparatusprovides the user information application apparatus with the list ofauthorized visited networks via a customized signaling message or asignaling message of the existing protocol (by adding new parameters andcorresponding values in the signaling message), for example, theServer-Assignment-Request/-Answer (SAR/SAA) of the Diameter protocol.

In the step 1 b, the user information storage apparatus may check inadvance whether the user is authorized to access the visited network. Ifyes, the user information storage apparatus returns the authenticationand/or authorization information and the list of authorized visitednetworks to the user; otherwise, it rejects the request forauthentication and/or authorization from the user informationapplication apparatus and may explain corresponding reasons.

Step 1 c: The user information application apparatus compares thevisited network identifier received in step 1 a with the information ofthe list of authorized visited networks received in step 1 b, and checkswhether the user is authorized to access the visited network.

Step 1 d: According to the checking result in step 1 c, if the user isvalid and authorized to access the visited network (for example, thevisited network is a RAN, or a core network or a CSN), the userinformation application apparatus returns an authentication and/orauthorization accept response to the user.

According to the checking result in step 1 c, if the user is notauthorized to access the visited network or the user is invalid, theuser information application apparatus returns an authentication and/orauthorization reject response to the user.

Optionally, in the accept and/or reject response, the user informationapplication apparatus sends the list of authorized visited networks tothe UE, and the UE updates the list of authorized visited networks whichis stored in the UE.

Optionally, the list of authorized visited networks sent to the UE maybe encrypted. For example, the list of authorized visited networks issent to the UE via an encrypted Diameter attribute value pair (AVP) or amessage of encrypted extensible authentication protocol (EAP).

FIG. 2 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with another embodiment of the presentinvention. The method may include the following steps:

Step 1: A WLAN AN and a 3GPP AAA Server perform an access authenticationand authorization procedure for a WLAN UE. If the identifier of the WLANAN selected by the user (WLAN UE) exists, it is also sent to the 3GPPAAA Server if necessary. In the case of roaming, the user selects a 3GPPvisited PLMN (VPLMN) as the path for the authentication and/orauthorization signaling. AAA messages transmitted from the WLAN UE andWLAN AN to the 3GPP AAA Server need to be forwarded through the 3GPP AAAProxy in the VPLMN. The AAA messages may also contain the 3GPP VPLMNidentifier.

Step 2: The 3GPP AAA Server obtains the security information forauthentication and authorization information for user authorization fromHLR/HSS. The authorization information contains a list of authorizedvisited networks for the user to access.

Step 3: The 3GPP AAA Server checks whether the user is valid and whetherit is authorized to access the visited network according to the securityinformation and authorization information obtained from the HLR/HSS.

Step 4: The 3GPP AAA Server returns an authentication and authorizationresponse to the WLAN UE according to the checking result in step 3. Itmay contain the list of authorized visited networks in the responsemessage.

FIG. 3 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with further another embodiment of thepresent invention. The method may include the following steps:

Step 1: An ASN gateway (ASN-GW) and a home CSN AAA Server perform anaccess authentication and authorization procedure for a mobilesubscriber station (MSS). If the identifier of the ASN selected by theuser (MSS) exists, it is also sent to the AAA Server if necessary. Inthe case of roaming, the user selects a visited CSN as the path forauthentication and authorization signaling. AAA messages transmittedfrom the MSS and ASN-GW to the home CSN AAA Server need to be forwardedby the visited CSN AAA Proxy in the visited network selected by theuser. The AAA messages may also contain the visited CSN identifier.

Step 2: The home CSN AAA Server obtains the security information forauthentication and the authorization information for authorization fromthe subscriber database. The authorization information contains the listof authorized visited networks for the user to access.

Step 3: The home CSN AAA Server checks whether the user is valid andwhether it is authorized to access to the visited network according tothe security information and the authorization information obtained fromthe subscriber database.

Step 4: The home CSN AAA Server returns an authentication andauthorization response to the MSS according to the checking result instep 3. It may contain the list of authorized visited networks in theresponse message.

During transmission of AAA messages and authentication messages, theASN-GW plays the role of a Network Access Server (NAS) and EAP proxy.Based on specific network structure and deployment, a base station (BS)can also play the role of an ASN-GW.

FIG. 4 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with further another embodiment of thepresent invention. The method may include the following steps:

Step 1 a: A RAN and a user information application apparatus perform anaccess authentication and authorization procedure for a UE. If theidentifier of the access network selected by the user (UE) exists, it issent to the user information application apparatus if necessary. Forexample, the WLAN identifier selected by the user to access the networkis a home WLAN identifier in the case of non-roaming or a roaming WLANidentifier in the case of roaming. In the case of roaming, theauthentication and/or authorization request contains the visited networkidentifier selected by the user and the user's permanent or temporaryidentity. In step 1 a, the user information application apparatus isoften an AAA server in the 3GPP system. For details about the visitednetwork identifier and user's identity, see the above description.

Step 1 b: The user information application apparatus detects whether theaccess network and/or core network selected by the user has changed. Ifyes, execute step 1 c.

Step 1 c: The user information application apparatus requests the userinformation storage apparatus to check whether the user is authorized toaccess the visited network.

Step 1 d: The user information storage apparatus checks whether the useris authorized to access the visited network.

This step may be triggered in the procedure in which the userinformation application apparatus obtains the authentication andauthorization information from the user information storage apparatus.For further details, refer to the embodiments showed with FIG. 5 andFIG. 6.

This step may also be triggered in the procedure in which the userinformation application apparatus sends an acknowledgement request tothe user information storage apparatus. For further details, refer tothe embodiments showed with FIG. 7, FIG. 8 and FIG. 9.

Step 1 e: If the user is authorized to access the visited network, theuser information storage apparatus returns an access accept message tothe user information application apparatus; otherwise, it returns anaccess reject message.

Step 1 f: If the user is valid and authorized to access the visitednetwork, the user information application apparatus returns an accessauthentication and authorization accept response to the user; if theuser is unauthorized to access the visited network or the user isinvalid, the user information application apparatus returns anauthentication and authorization reject response to the user.

FIG. 5 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with further another embodiment of thepresent invention. Assuming that the visited network selected by theuser has changed in this embodiment and the method may include thefollowing steps:

Step 1: A WLAN UE has been authenticated and authorized to accessservices through WLAN AN 1.

Step 2: Due to some special reasons, such as handoff, the WLAN UE needsto access a network through WLAN AN 2. Therefore, WLAN AN 2 and 3GPP AAAServer perform an authentication and authorization procedure for theWLAN UE. The identifier of the WLAN AN 2 selected by the user is sent tothe 3GPP AAA Server if necessary. In the case of roaming, the userselects a 3GPP VPLMN as the path for the authentication andauthorization signaling. AAA messages transmitted from the WLAN UE andWLAN AN to the 3GPP AAA Server need to be forwarded through the 3GPP AAAProxy which is located in the 3GPP VPLMN in the case of roaming. TheseAAA messages may contain the 3GPP VPLMN identifier.

Step 3: The 3GPP AAA Server detects that the WLAN AN selected by theuser has changed according to the identifier of WLAN AN 2 obtained instep 2 and requests the HLR/HSS to check whether the user is authorizedto access WLAN AN 2.

If the 3GPP AAA Server stores the authentication and authorizationinformation of the user, it only needs to send an acknowledgementrequest to the HLR/HSS without obtaining the authentication andauthorization information from the HLR/HSS; if the 3GPP AAA Server doesnot store the authentication and authorization information of the useror the stored information is no longer valid, it needs to obtain theauthentication and authorization information of the user from theHLR/HSS if necessary.

The 3GPP AAA Server sends an acknowledgement request to the HLR/HSS,asking the HLR/HSS to check whether the user is authorized to accessWLAN AN 2. The acknowledgement request can be carried via new parametersof Server-Assignment-Type of the SAR/SAA message.

If the 3GPP AAA Server does not have available authenticationinformation, it obtains authentication information from the HSS. Duringthe process, the HLR/HSS checks whether the user is authorized to accessthe visited network. If the 3GPP AAA Server does not have availableauthorization information, it may send an authorization request to theHSS to obtain authorization information. During the process, the HLR/HSSmay check whether the user is authorized to access the visited network.

Step 4: The HLR/HSS checks whether the user is authorized to access WLANAN 2 according to the stored list of authorized visited WLANs for theuser to access. If the user is not authorized, the HLR/HSS returns areject response to the 3GPP AAA Server and does not return the requestedauthentication and authorization information; if the user is authorized,the HLR/HSS returns an access accept message to the 3GPP AAA Server. TheHLR/HSS also returns security information used for authentication andauthorization information to the 3GPP AAA Server.

Step 5: If the 3GPP AAA Server receives an access accept message fromthe HLR/HSS and checks that the user is valid by using the securityinformation and authorization information obtained from the HLR/HSS, itreturns an authentication and authorization accept response to the WLANUE; otherwise, it returns a reject response to reject the WLAN UE toaccess the network through WLAN AN 2.

FIG. 6 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with further another embodiment of thepresent invention. The method may include the following steps:

Step 1: A WLAN UE has been authenticated and authorized through a WLANAN and a VPLMN1, and the WLAN UE can access to services through the WLANAN.

Step 2: In the case of roaming, the user (WLAN UE) selects a 3GPP VPLMNas the path for the authentication and authorization signaling. AAAmessages transmitted from the WLAN UE and WLAN AN to a 3GPP AAA Serverneed to be forwarded through the 3GPP AAA Proxy in the 3GPP VPLMN. TheAAA messages may also contain the 3GPP VPLMN identifier. Due to somespecial reasons such as handoff, the WLAN UE needs to access the networkthrough VPLMN2. Therefore, a VPLMN2 and the 3GPP AAA Server perform anauthentication and authorization procedure for the WLAN UE. If theidentifier of the WLAN AN selected by the user exists, it may also besent to the 3GPP AAA Server if necessary.

Step 3: After detecting that the VPLMN selected by the user has changedaccording to the identifier of the VPLMN obtained in step 2, the 3GPPAAA Server obtains authentication and authorization information from aHLR/HSS no matter whether it has the authentication and authorizationinformation of the user, for example, if the 3GPP server has unusedauthentication vectors, it needs to obtain the authentication andauthorization information.

If the 3GPP AAA Server detects that the VPLMN selected by the user hasnot changed; but it does not store the authentication and authorizationinformation of the user or the stored authentication and authorizationinformation is no longer valid, the 3GPP AAA Server also needs to obtainthe information form the HLR/HSS if necessary.

Step 4: The HLR/HSS checks whether the user is authorized to accessVPLMN2 according to the stored list of authorized visited networks. Ifthe user is not authorized to access the VPLMN2, the HLR/HSS returns areject response to the 3GPP AAA Server and does not return the requestedauthentication and authorization information; if the user is authorizedto access the VPLMN2, the HLR/HSS returns an access accept message tothe 3GPP AAA Server and returns security information used forauthentication and authorization information to the 3GPP AAA Server.

Step 5: If the 3GPP AAA Server receives the access accept message fromthe HLR/HSS and checks that the user is valid according to the securityinformation and authorization information obtained from the HLR/HSS, itreturns an authentication and authorization accept response to the WLANUE; otherwise, it returns a reject response to the WLAN UE, not allowingthe WLAN UE to access the network through VPLMN2.

FIG. 7 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with further another embodiment of thepresent invention. The method may include the following steps:

Step 1: Substantially same as step 1 a of the embodiment showed in FIG.4.

Step 2: The user information application apparatus detects whether theaccess network and/or core network selected by the user has changed. Ifchanged, execute step 3; otherwise, execute step 4.

Step 3: If authentication and/or authorization information are availablein the user information application apparatus, the user informationapplication apparatus may send an acknowledgement request to the userinformation storage apparatus, asking the user information storageapparatus to check whether the user is authorized to access the visitednetwork. For example, the acknowledgement request may be sent to the HSSvia a Diameter RAR/RAA message.

If the authentication information is not available in the userinformation application apparatus, the user information applicationapparatus may send an authentication request to the user informationstorage apparatus to obtain the authentication information. During theprocess, the user information storage apparatus checks whether the useris authorized to access the visited network.

If the authorization information is not available in the userinformation application apparatus, the user information applicationapparatus may send an authorization request to the user informationstorage apparatus to obtain the authorization information. During theprocess, the user information storage apparatus may also check whetherthe user is authorized to access the visited network.

Step 4: Substantially same as step 1 f of the embodiment showed in FIG.4

FIG. 8 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with further another embodiment of thepresent invention. Assuming that the visited network selected by theuser has changed in this embodiment and the method may include thefollowing steps:

Steps 1-3: Substantially same as steps 1-3 of the embodiment showed inFIG. 5.

Step 4: The 3GPP AAA Server sends a request containing the WLANidentifier to the HLR/HSS. The HLR/HSS checks whether the user isauthorized to access the visited network according to the stored list ofvisited networks authorized and returns a response to the 3GPP AAAServer.

Step 5: Substantially same as step 5 of the embodiment showed in FIG. 5.

FIG. 9 shows a simplified flowchart illustrating a method for accessinga visited network in accordance with further another embodiment of thepresent invention. Assuming that the visited network selected by theuser has changed in this embodiment; and the method may include thefollowing steps:

Steps 1-3: Substantially same as steps 1-3 of the embodiment showed inFIG. 6.

Step 4: The 3GPP AAA Server sends a request containing the VPLMNidentifier to the HLR/HSS. The HLR/HSS checks whether the user isauthorized to access the visited network according to the stored list ofauthorized visited networks and returns a response to the 3GPP AAAServer.

Step 5: Substantially same as step 5 of the embodiment showed in FIG. 6.

Embodiments of the present invention showed in FIG. 6 and FIG. 9 differfrom embodiments showed in FIG. 5, FIG. 7, and FIG. 8. It says in thefollowing:

In the embodiments showed in FIG. 6 and FIG. 9, if the 3GPP AAA Serverdetects that the visited network selected by the user has changed, itobtains the authentication and authorization information from the HSS nomatter whether it has available authentication and authorizationinformation. During the process, the HSS checks whether the user isauthorized to access the visited network. This checking procedure, forexample, is implemented via Diameter SAR/SAA messages.

In the embodiments showed in FIG. 5, FIG. 7 and FIG. 8, if the 3GPP AAAServer detects that the visited network selected by the user has changedand it has available authentication and authorization information, itsends an acknowledgement request to the HSS, asking the HSS to checkwhether the user is authorized to access the visited network withoutobtaining authentication and authorization information from the HSS.This checking procedure, for example, can be implemented via DiameterRAR/RAA messages.

Embodiments of the present invention also provide methods for updatingthe list of authorized visited networks stored in the UE. Three examplesare as follows:

Method 1: A UE initiates a request for updating the list of authorizedvisited networks for the user to access periodically (refer to FIG. 10),which may include the following steps:

2 a. A RAN and a user information application apparatus perform anaccess authentication and authorization procedure for the UE.

2 b. The UE sends a request for updating the list of authorized visitednetworks to the user information application apparatus, asking the userinformation application apparatus to provide the list of authorizedvisited networks to the user. The request contains the user's permanentor temporary identity.

2 c. Optionally, the user information application apparatusauthenticates and authorizes the user and checks whether the user isvalid (The user information application apparatus may interact with theuser information storage apparatus in the process). If the user isinvalid, the user information application apparatus returns a rejectresponse to the UE, which may include the reason of reject, andterminates the subsequent process; if the user is valid, the userinformation application apparatus executes the steps below. If the abovestep 2 a is executed, step 2 c may be omitted.

2 d. The user information application apparatus obtains the list ofauthorized visited networks from a user information storage apparatus.In the process, the user information storage apparatus provides the userinformation application apparatus with the list of authorized visitednetworks via a customized signaling message or a signaling message ofthe existing protocol (by adding new parameters and corresponding valuesin the signaling message), for example, SAR/SAA message of the Diameterprotocol.

2 e. The user information application apparatus returns a responsemessage to the UE. The response message contains the list of authorizedvisited networks.

Optionally, the list of authorized visited networks, sent to the UE maybe encrypted, for example, via an encrypted Diameter AVP or a message ofencrypted EAP.

Method 2: The user information storage apparatus sends a notificationfor updating the list of authorized visited networks for the user toaccess (refer to FIG. 11), which may include the following steps:

3 a. A RAN and a user information application apparatus perform anaccess authentication and authorization procedure for the UE.

3 b. The user information storage apparatus sends a notification forupdating the list of authorized visited networks to the user informationapplication apparatus, which contains the user's permanent or temporaryidentity, asking the user information application apparatus to notifythe user to update the list of authorized visited networks.

3 c. The user information application apparatus checks whether the useris online. If online, it sends the update notification to the UE; ifoffline, it returns a response to the user information storageapparatus, informing that the user is offline and cannot be notified.The user information application apparatus may also store the updatenotification temporarily for some time. If the user is online in theperiod, the user information application notifies the user; otherwise,it returns a response to the user information storage apparatus,informing that the user cannot be notified.

3 d. Upon receiving the update notification, the UE sends a request forupdating the list of visited networks authorized to the user informationapplication apparatus, asking the user information application apparatusto provide the list of authorized visited networks. The request containsthe user's permanent or temporary identity.

3 e. Optionally, the user information application apparatusauthenticates and authorizes the user and checks whether the user isvalid (The user information application apparatus may interact with theuser information storage apparatus in the procedure). If the user isinvalid, the user information application apparatus returns a rejectresponse to the UE, which may include the reason of reject, andterminates the subsequent process; if the user is valid, the userinformation application apparatus executes the steps below. If the abovestep 3 a is executed, step 3 e may be omitted.

3 f. The user information application apparatus obtains the list ofauthorized visited networks from the user information storage apparatus.In the procedure, the user information storage apparatus provides theuser information application apparatus with the list of authorizedvisited networks via a customized signaling message or a signalingmessage of the existing protocol (by adding new parameters andcorresponding values), for example, a SAR/SAA message or an AAR/AAAmessage of the Diameter protocol.

3 g. The user information application apparatus returns a responsemessage to the UE. The response message contains the list of authorizedvisited networks.

Optionally, the list of authorized visited networks sent to the UE maybe encrypted, for example, via an encrypted Diameter AVP or an encryptedEAP message.

Method 3: The user information storage apparatus pushes the list ofauthorized visited networks (refer to FIG. 12), which may include thefollowing steps:

4 a. A RAN and a user information application apparatus perform anaccess authentication and authorization procedure for a UE.

4 b. The user information storage apparatus pushes the updated list ofauthorized visited networks (containing the user's permanent ortemporary identity) to the user information application apparatus,asking the user information application apparatus to notify the user toupdate the list of authorized visited networks.

The user information storage apparatus may push the list of authorizedvisited networks to the user information application apparatus via acustomized signaling message or a signaling message of the existingprotocol (by adding new parameters and corresponding values), forexample, a SAR/SAA message or an AAR/AAA message of the Diameterprotocol or a Change-of-Authorisation (CoA) message of the RADIUSprotocol.

4 c. The user information application apparatus pushes the updated listof visited networks authorized to the UE.

The user information application apparatus may push the list ofauthorized visited networks to the UE via a customized signaling messageor a signaling message of the existing protocol (by adding newparameters and corresponding values), for example, aPush-Profile-Request/-Answer(PPR/PPA) message or a SAR/SAA message ofthe Diameter protocol or a CoA message of the RADIUS protocol.

Optionally, the list of authorized visited networks sent to the UE maybe encrypted, for example, via an encrypted Diameter AVP or an encryptedEAP message.

4 d. Optionally, after the UE has updated the list of authorized visitednetworks, the UE returns an update acknowledgement message to the userinformation application apparatus. Then, the user informationapplication apparatus sends the acknowledgement message to the userinformation storage apparatus.

In the flows of 2 a-2 e, 3 a-3 g and 4 a-4 d, the user informationapplication apparatus may be an AAA server, or a dedicated applicationserver used for user software and information upgrade, or a commonapplication server, and the user information storage apparatus may be anHLR, or an HSS, or a database for storing user information.

FIG. 13 shows a schematic diagram of a user information applicationapparatus according to an embodiment of the present invention. The userinformation application apparatus includes:

an authentication and authorization module 11;

a detecting module 12; and

a checking module 13.

The authentication and authorization module 11 is adapted to receive anaccess authentication and/or authorization request initiated by a user,check whether the user is valid according to an authentication and/orauthorization information of the user, and return an authenticationand/or authorization accept or reject response to the user according tothe result of checking whether the user is authorized to access thevisited network by the checking module 13.

The detecting module 12 is adapted to detect whether the visited networkselected by the user has changed. If the visited network has changed,the checking module 13 is triggered.

The checking module 13 is adapted to obtain a list of authorized visitednetworks from the user information storage apparatus 2 and check whetherthe user is authorized to access the visited network according to theinformation of the list of authorized networks; or the checking module13 is adapted to request the user information storage apparatus 2 tocheck whether the user is authorized to access the visited network andsend the checking result to the authentication/authorization module 11.

The checking module 13 may include:

an obtaining sub-module 131, which is adapted to obtain the list ofauthorized visited networks from the user information storage apparatus2 and stores the list;

a checking sub-module 132, which is adapted to check whether the user isauthorized to access the visited network according to the obtained listof authorized visited networks;

a sending sub-module 133, which is adapted to send the checking resultof the checking sub-module 132 to the authentication and authorizationexecution module 11.

The checking module 13 may also include:

a requesting sub-module 134, which is adapted to send an acknowledgementrequest message containing the identifier of the visited network to theuser information storage apparatus 2, requesting the user informationstorage apparatus 2 to check whether the user is authorized to accessthe visited network;

a receiving sub-module 135, which is adapted to receive the result ofchecking whether the user is authorized to access the visited network bythe user information storage apparatus 2.

The sending sub-module 133, which is adapted to send the checking resultof the receiving sub-module 135 to the authentication and authorizationexecution module 11.

FIG. 14 shows a schematic diagram of a user information storageapparatus according to an embodiment of the present invention. The userinformation storage apparatus includes:

a storage module 21; and

an information sending module 23.

The storage module 21 is adapted to store a list of authorized visitednetworks and the authentication and/or authorization information of auser.

The information sending module 23 is adapted to send the list of visitednetworks authorized and authentication and/or authorization informationof the user to the user information application apparatus 1.

The user information storage apparatus may also include an acknowledgingmodule 22:

The acknowledging module 22 is adapted to receive an acknowledgementrequest message containing the identifier of the visited network fromthe user information application apparatus 1, check whether the user isauthorized to access the visited network according to the list ofauthorized visited networks stored in the storage module 21, and sendthe checking result to the information sending module 23.

The information sending module 23 is adapted to send the checking resultof the acknowledging module 22 to the user information applicationapparatus 1.

FIG. 15 shows a schematic diagram of a system 3 for accessing a visitednetwork according to an embodiment of the present invention. The system3 may include:

a user information application apparatus 1; and

a user information storage apparatus 2.

The user information storage apparatus and the user informationapplication apparatus may be independent network entities and setseparately as required, for example, a HLR/HSS as the user informationstorage apparatus and a 3GPP AAA Server as the user informationapplication apparatus in a 3GPP system; or integrated in a functionalentity and serve as different logical units of the functional entity,between which the interfaces are internal interfaces.

To sum up, when a user selects a visited network and initiates anauthentication and authorization request, the embodiment of the presentinvention provides effective authentication and authorization signalingflows. The method provided by the embodiment of the present inventioncan effectively check whether the user is authorized to access thevisited network.

The embodiment of the present invention also provides three methods forupdating the list of authorized visited networks stored in the UE sothat the list of authorized visited networks stored in the UE can beupdated synchronously with the visited networks authorized by theoperator.

Although the present invention has been illustrated and described withreference to some preferred embodiments, the present invention is notlimited to these. Those skilled in the art may make various variationsand modifications without departing from the spirit and scope of theinvention. The present invention shall cover these modifications andvariations

What is claimed is:
 1. A method for accessing a visited network,comprising: receiving, by an authentication, authorization andaccounting (AAA) server device, an access request initiated by a userfor selecting a visited network; detecting, by the AAA server device,whether the visited network selected by the user has changed; if thevisited network selected by the user has changed, requesting, by the AAAserver device, a home subscriber server (HSS) to check whether the useris authorized to access the visited network according to a list ofauthorized visited networks; and if the user is authorized to access thevisited network, returning, by the AAA server device, an access acceptresponse to the user to allow the user to access the visited network; ifthe visited network selected by the user has not changed, checking, bythe AAA server device, whether the user is valid and authorized toaccess the visited network; and if the user is valid and authorized toaccess the visited network, returning, by the AAA server device, theaccess accept response to the user; checking, by the AAA server device,that the user is valid in response to a request sent from the user forupdating the list of authorized visited networks according to a presetperiod; and sending, by the AAA server device, the list of authorizedvisited networks, which is stored in the AAA server device or obtainedfrom the HSS, to the user.
 2. The method of claim 1, wherein the accessrequest is an authentication and authorization request; and the accessaccept response is an authentication and authorization access acceptresponse.
 3. The method of claim 1, wherein requesting, by the AAAserver device, the HSS to check whether the user is authorized to accessthe visited network further comprises: sending, by the AAA serverdevice, an acknowledgement request containing an identifier of thevisited network selected by the user to the HSS for checking whether theuser is authorized to access the visited network according to the listof authorized visited networks.
 4. The method of claim 1, whereinrequesting, by the AAA server device, the HSS to check whether the useris authorized to access the visited network further comprises:initiating, by the AAA server device, a request for obtainingauthentication and authorization information to the HSS, and forrequesting the HSS to check whether the user is authorized to access thevisited network according to the list of authorized visited networks. 5.The method of claim 1, wherein the method further comprises: checking,by the AAA server device, whether the authentication and authorizationinformation of the user is stored therein; if the authentication andauthorization information of the user is stored in the AAA serverdevice, sending, by the AAA server device, an acknowledgement requestcontaining the identifier of the visited network to the HSS forrequesting the HSS to check whether the user is authorized to access thevisited network according to the list of authorized visited networks;returning, by the HSS, an access accept response or reject response tothe AAA server-device according to checking result of the HSS; if theauthentication and authorization information of the user is not storedin the AAA server device, initiating, by the AAA server device, arequest for obtaining the authentication and authorization informationto the HSS and for requesting the HSS to check whether the user isauthorized to access the visited network according to the list ofauthorized visited networks; returning, by the HSS, the authenticationand authorization information of the user and the access accept responseor a reject response to the AAA server device according to checkingresult of the HSS.
 6. The method of claim 5, wherein the acknowledgementrequest is sent to the HSS via a customized signaling message, idle ornew parameters of an existing protocol signaling message.
 7. The methodof claim 1, wherein the list of authorized visited networks of the usercomprises at least one of authorized visited access network identifiersand authorized visited core network identifiers.
 8. An authentication,authorization and accounting (AAA) server device, comprising: areceiver, configured to receive an access request initiated by a userfor selecting a visited network; and a processor, configured to: detectwhether the visited network selected by the user has changed; if thevisited network selected by the user has changed, the processer isfurther configured to request a home subscriber server (HSS) to checkwhether the user is authorized to access the visited network accordingto a list of authorized visited networks; and if the user is authorizedto access the visited network, the processer is further configured toreturn an access accept response to the user to allow the user to accessthe visited network; if the visited network selected by the user has notchanged, the processer is further configured to check whether the useris valid and authorized to access the visited network; and if the useris valid and authorized to access the visited network, the processer isfurther configured to return the access accept response to the user;check that the user is valid in response to a request sent from the userfor updating the list of authorized visited networks according to apreset period; and send the list of authorized visited networks, whichis stored in the AAA server device or obtained from the HSS, to theuser.
 9. The AAA server device of claim 8, wherein the access request isan authentication and authorization request; and the access acceptresponse is an authentication and authorization access accept response.10. The AAA server device of claim 8, wherein the processer is furtherconfigured to send an acknowledgement request containing an identifierof the visited network selected by the user to the HSS for checkingwhether the user is authorized to access the visited network accordingto the list of authorized visited networks.
 11. The AAA server device ofclaim 8, wherein the processer is further configured to initiate arequest for obtaining authentication and authorization information tothe HSS and for requesting the HSS to check whether the user isauthorized to access the visited network according to the list ofauthorized visited networks; and the receiver is further configured toreceive the authentication and authorization information of the user ifthe user is authorized to access the visited network.
 12. A system foraccessing a visited network, comprising: an authentication,authorization and accounting (AAA) server device communicating with ahome subscriber server (HSS); wherein the AAA server device isconfigured to: receive an access request initiated by a user forselecting a visited network; and detect whether the visited networkselected by the user has changed; if the visited network selected by theuser has changed, the AAA server device is further configured to requestthe HSS to check whether the user is authorized to access the visitednetwork according to a list of authorized visited networks; and if theuser is authorized to access the visited network, the AAA server deviceis further configured to return an access accept response to the user toallow the user to access the visited network; if the visited networkselected by the user has not changed, the AAA server device is furtherconfigured to check whether the user is valid and authorized to accessthe visited network; and if the user is valid and authorized to accessthe visited network, the AAA server device is further configured toreturn the access accept response to the user; check that the user isvalid in response to a request sent from the user for updating the listof authorized visited networks according to a preset period; and sendthe list of authorized visited networks, which is stored in the AAAserver device or obtained from the HSS, to the user.
 13. The system ofclaim 12, wherein the access request is an authentication andauthorization request; and the access accept response is anauthentication and authorization access accept response.
 14. The systemof claim 12, wherein the AAA server device is further configured to sendan acknowledgement request containing an identifier of the visitednetwork selected by the user to the HSS for checking whether the user isauthorized to access the visited network according to the list ofauthorized visited networks.
 15. The system of claim 12, wherein the AAAserver device is further configured to initiate a request for obtainingauthentication and authorization information to the HSS and forrequesting the HSS to check whether the user is authorized to access thevisited network according to the list of authorized visited networks;and the AAA server device is further configured to receive theauthentication and authorization information of the user if the user isauthorized to access the visited network.